The present invention relates to a liquid crystal optical device for use in a liquid crystal display device, optical shutter array, etc., and more particularly to a liquid crystal optical device having improved display and driving characteristics.
Hitherto, there has been known a type of liquid crystal device which utilizes a TN (twisted namatic) liquid crystal, as shown in "Voltage-Dependent Optical Activity of a Twisted Nematic Liquid Crystal" by M. Schadt and W. Helfrich, Applied Physics Letters Vol. 18, No. 4 (Feb. 15, 1971) pp. 127-128. In this type of liquid crystal device, however, when a matrix electrode structure is to be driven according to a time division scheme, the number of picture elements has been restricted because of generation of crosstalk.
As another type of liquid crystal device, there has been known one comprising a plurality of picture elements each connected and subjected to switching by a thin film transistor switching element. This type of display device involves a problem that forming thin film transistors on a substrate or base plate is difficult and it is also difficult to prepare a large display area of display devices.
In order to obviate the above-mentioned drawbacks of the conventional types of liquid crystal devices, Clark and Lagerwall have proposed the use of a liquid crystal device using a bistable liquid crystal (Japanese Laid-Open Patent Application No. 107216/1981, U.S. Pat. No. 4,367,924, etc.). As the bistable liquid crystal, a ferroelectric liquid crystal having a chiral smectic C (SmC*) phase or H (SmH*) phase is generally used. The ferroelectric liquid crystal has bistability including a first stable state and a second stable state. Accordingly, different from the conventional TN-type liquid crystal in the above-mentioned device, the liquid crystal is oriented to the first stable state in response to one electric field vector and to the second stable state in response to the other electric field vector. Further, this type of liquid crystal very quickly assumes either one of the above-mentioned two stable states in reply to an electric field applied thereto and retains the state in the absence of an electric field. By utilizing these properties, essential improvements can be attained with respect to the above-mentioned difficulties involved in the conventional TN-type liquid crystal device. This point will be explained in further detail hereinafter in connection with the present invention. However, such a ferroelectric liquid crystal device having
bistability can be generally realized when the cell thickness is 2 .mu.m or less, and a high contrast display cannot be attained with a larger cell thickness.